Constant current regulators (CCRs) are used to convert an input AC voltage into an output AC current in order to provide power to constant current loads, such as airfield lighting series circuits. Typically, the primary source of input power for constant current regulators is provided by the local utility. A secondary source of input power may be a generator or a separate feeder from the local utility. During certain situations, it may be advantageous to remotely switch from the primary power source to the secondary source. For example, in the airfield environment, it may be advantageous to switch from receiving power from the local utility to receiving power from a generator during low visibility or other poor weather conditions, as the generator may be more reliable than the local utility under such circumstances.
One method of switching from the input contacts of one power source to the input contacts of another power source is a “break-before-make” operation, in which the first power source is disconnected from the constant current regulator before the second power source is connected to the constant current regulator. During the transition period, the input power drops to zero. The transition period may vary, often lasting between 25 milliseconds to hundreds of milliseconds. In certain cases, the transition period is long enough for the constant current regulator to dissipate its internal energy and the constant current regulator may turn off and reset. Typically, the time for a constant current regulator to return to full current after a reset is five seconds. In certain applications, such a delay is longer than is desirable. However, when the transition time is less than the time required for the constant current regulator to dissipate its internally stored energy, the constant current regulator may generate large output current spikes that may be detrimental to the load.